The development of smaller and smaller transistors has led to the architecture of the transistors being changed in order to overcome certain problems, particularly Short Channel Effects (SCEs) or Drain Induced Barrier Lowering (DIBL). In particular, fully depleted architectures have been employed in order to avoid these effects. At the same time, however, the performance improvement of transistors has led to attempts at replacing silicon by germanium, which has a lower resistivity. The development of a transistor whose channel comprises germanium and is produced on an insulating layer therefore presents a significant benefit, and would make it possible to obtain a transistor with enhanced performance.
One conventional method for producing such an architecture is presented in the article “High-Mobility Strained SiGe-on-Insulator pMOSFETs With Ge-Rich Surface Channels Fabricated by Local Condensation Technique” by Tezuka et al. (IEEE, Electron Device Letters, Vol. 26, No 4, April 2005). The article generally proposes a method for producing a transistor on a silicon-on-insulator substrate, wherein a silicon-germanium layer is deposited on the substrate and is covered with a silicon layer then with a silicon oxide layer. Oxidation of the silicon is then carried out so as to oxidize a part of the substrate lying between the insulator of the substrate and the silicon oxide layer. The authors then obtain a germanium-rich layer between the insulating layer of the substrate and the silicon oxide layer which has been formed during the oxidation. The silicon oxide layer is etched so as to form the gate insulator, then the gate and the source and drain regions are formed in order to obtain the transistor.
However, conventional methods have several drawbacks which limit its use. First, conventional methods require the production of the transistor on a silicon-on-insulator substrate. Thus, the underlying silicon of the substrate is also oxidized during the oxidation of the silicon of the silicon-germanium. It is therefore difficult to implement such a method on a silicon substrate, since there would no longer be an insulating layer allowing the germanium atoms to be stopped and confined during the oxidation phase.
Furthermore in conventional methods, oxidation of the silicon causes migration of the silicon atoms towards the oxidized surface, whereas the germanium atoms are repelled in the opposite direction. These movements of atoms do not guarantee a good surface quality between the germanium-rich layer and the silicon oxide layer which is formed during the oxidation. However, this interface is important since the germanium-rich layer is used as the channel of the transistor and a part of the silicon oxide layer is used as the gate insulator. The appearance of electrical defects due to surface defects between the channel and the gate insulator is therefore possible.
There is therefore a need for a system and method for producing a transistor with a germanium-rich channel and with a fully depleted architecture. In particular, there is a need for a system and method which can produce such a transistor easily on any type of substrate and which the formation of the channel can be easily controlled